Self-positioning electrode system and method for renal nerve modulation

ABSTRACT

Systems for nerve and tissue modulation are disclosed. An example system may include an intravascular nerve modulation system including an elongated shaft having a proximal end region and a distal end region. The system may include an expandable frame having one or more electrodes positioned on or about the frame. An actuation assembly including a biasing element, a central shaft, and a piston may be configured to provide for controlled expansion of the expandable frame. The system may further include a control element for controlling the actuation assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S. Provisional application Ser. No. 61/702,065, filed Sep. 17, 2012, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices and methods for making and using medical devices. More particularly, the present disclosure pertains to medical devices and methods for performing renal nerve modulation.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed tier medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured. by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices.

SUMMARY

This disclosure is directed to several alternative designs, materials and use alternatives for medical device structures and assemblies. An example device may include a system for nerve modulation. The system may include an elongate shaft having a proximal end, a distal end and a lumen extending therebetween. An expandable frame having a proximal end and a. distal end may be positioned adjacent to the distal end of the elongate shaft. The expandable frame may be configured to shift between an expanded configuration and a collapsed configuration. The expandable frame may include a plurality of ribbons extending between a proximal end and a distal end of the expandable frame. At least one of the ribbons may include an electrode positioned at a location radially inwards relative to the greatest radial extent of the expandable frame. The modulation system may further include an expansion mechanism configured to move the expandable frame between the collapsed and expanded configurations. The expansion mechanism may include a piston movably disposed within the lumen of the elongate shaft and a central shaft having a distal end attached to the distal end of the expandable frame and a proximal end attached to the piston. The expansion mechanism may further include a biasing element situated between the distal end of the elongate shaft and the piston. The expansion system may further include a control element extending proximally from a proximal end of the piston.

The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings.

FIG. 1 is a schematic view illustrating a renal nerve modulation system in situ.

FIG. 2 is a partial cross-section of an illustrative intravascular nerve modulation system.

FIG. 3 is a graphical representation of the forces on an example expandable frame as a function of the diameter of the frame.

FIG. 4 is a partial cross-sectional side view of example medical device in a firs t configuration.

FIG. 5 is a partial cross-sectional. side view of an example medical device in a second configuration.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DETAILED DESCRIPTION

For the Mowing defined terms, these definitions shah be applied, unless a different definition is given in the claims or elsewhere in this specification.

All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result), In many instances, the terms “about” may be indicative as including numbers that are rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

Although some suitable dimensions ranges and/or values pertaining to various components, features and/or specifications are disclosed, one of the skill in the art, incited by the present disclosure, would understand desired dimensions, ranges and/or values may deviate from those expressly disclosed. As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise, As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

For purposes of this disclosure, “proximal” refers to the end closer to the device operator during use, and “distal” refers to the end farther from the device operator during use.

The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The detailed description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. The illustrative embodiments depicted are intended only as exemplary. Selected features of any illustrative embodiment may be incorporated into an additional embodiment unless clearly stated to the contrary.

It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with one embodiment, it should be understood that such feature, structure, or characteristic may also be used in connection with other embodiments whether or not explicitly described unless cleared stated to the contrary.

Certain treatments require the temporary or permanent interruption or modification of select nerve function. One example treatment is renal nerve ablation, which is sometimes used to treat conditions related to congestive heart failure or To hypertension. The kidneys produce a sympathetic response to congestive heart failure, which, among other effects, may increase the undesired retention of water and/or sodium. Ablating some of the nerves running to the kidneys may reduce or eliminate this sympathetic function, which may provide a corresponding reduction in the associated undesired symptoms.

While the devices and methods described herein are discussed relative to renal nerve modulation, it is contemplated that the devices and methods may be used in other locations and/or applications where nerve modulation and/or other tissue modulation including, but not limited to, heating, activation, blocking, disrupting, or ablation are desired, such as, but not limited to: blood vessels, urinary vessels, or in other tissues via trocar and cannula access. For example, the devices and methods described herein can be applied to hyperplastic tissue ablation, tumor ablation, benign prostatic hyperplasia therapy, nerve excitation or blocking or ablation, modulation of muscle activity, hyperthermia or other warming of tissues, etc. It is further contemplated that the devices and methods described herein may be used in other locations and/or applications where controlled expansion of a framework or ablation is desired. For example, the devices and method described herein may be used in vein ablation for vein closure or in the pulmonary arterial ostium for tachycardia. In some instances, it may be desirable to ablate perivascular renal nerves with radiofrequency (RF) energy. The term modulation refers to ablation and other techniques that may alter the function of nerves and other tissue such as brain tissue or cardiac tissue. When multiple ablations are desirable, they may be performed sequentially by a single ablation device.

FIG. 1 is a schematic view of an illustrative renal nerve modulation system 10 in situ. System 10 may include one or more conductive power elements 12, a central elongate shaft 14, a sheath 16, a control and power block 18 and return electrode patches 20A and 20B, (collectively, electrode patches 20). The element 12 provides power to an electrode or other modulation element disposed adjacent to, about, and/or within the central elongate shaft 14 and, optionally, within the sheath 16, the details of which can be better seen in subsequent figures. A proximal end of element 12 may be connected to a. control and power block 18, which supplies the necessary electrical energy to activate the one or more electrodes at or near a distal end of the element 12. The control and power block 18 may include monitoring elements to monitor parameters such as power, temperature, voltage, pulse size and/or frequency and other suitable parameters as well as suitable controls for performing the desired procedure. in some instances, the power element block 18 may control an ablation electrode. The ablation electrode may be configured to operate at a frequency of about 460 kilohertz (KHz). It is contemplated that any desired frequency may be used, for example, from 450-500 KHz. In addition, it is contemplated that frequencies outside this range may also be used, as desired. It is further contemplated that the perivascular nerves may be ablated by other means including application of thermal, ultrasound, laser, microwave, and other related energy sources to the target region and these devices may require that power be supplied by the power block 18 in a different form. In some instances, return electrode patches 20 may be connected to the control and power block 18 and may be supplied on the legs and/or at another conventional location on the patient's body to complete the circuit.

FIG. 2 illustrates a distal portion of an intravascular nerve modulation system 200. The nerve modulation system 200 may be configured to be advanced within a body lumen having a vessel wall 202, which may be surrounded by local body tissue, including adventitia and connective tissues, nerves, fat, fluid, etc., in addition to the muscular vessel wall. A portion of the surrounding tissue may be the desired treatment region. As shown, the system 200 may include an elongate shaft 211 having a distal end region 204. The elongate shaft 211 may extend proximally from the distal end region 204 to a proximal end region (not shown) configured to remain outside of a patient's body. The proximal end of the elongate shaft 211 may include a hub (not shown) attached thereto for connecting other diagnostic and/or treatment devices for providing a port for facilitating other interventions. In some instances, the elongate shaft 211 may be advanced to a desired region within an outer sheath or guide catheter 214, although this is not required.

The elongate shaft 211 may have a long, thin, flexible tubular configuration. A person skilled in the art will appreciate that other suitable configurations such as, but not limited to, rectangular, oval, irregular, or the like may also be contemplated. In addition, the elongate shaft 211 may have a cross-sectional configuration adapted to be received in a desired vessel, such as a renal artery. For instance, the elongate shaft 211 may be sized and configured to accommodate passage through the intravascular path, which leads from o percutaneous access site in, for example, the femoral, brachial, or radial artery, to a targeted treatment site, for example, within a renal artery.

It is contemplated that the stiffness of the elongate shaft 211 may be modified to form a modulation system 200 for use in various vessel diameters. To this end, the material used for manufacturing the elongate shaft 211 may include any suitable biocompatible material such as, but are not limited to, polymers, metals, or alloys, either in combination or alone. The material employed may have enough stiffness for use in various lumen diameters, and sufficient flexibility to maneuver through tortuous and/or stenotic lumens, avoiding any undesirable tissue injuries.

The elongate shaft 211 may further include one or more lumens, such as lumen 215, extending therethrough. For example, the elongate shaft 211 may include a guidewire lumen and/or one or more auxiliary lumens. The lumens may have a variety of configurations and/or arrangements. For example, a guidewire lumen may extend the entire length of the elongate shaft 211 such as in an over-the-wire catheter or may extend only along a distal portion of the elongate shaft 211 such as in a single operator exchange (SOE) catheter. These examples are not intended to be limiting, but rather examples of some optional configurations. While not explicitly shown, the modulation system 200 may include temperature sensor/wire, an infusion lumen, radiopaque marker bands, fixed guidewire tip, a guidewire lumen, external sheath, and/or other components to facilitate the use and advancement of the system 200 within the vasculature.

The modulation system 200 may further include an expandable frame 208, a central shaft 210, a control element 212, and an actuation assembly 401. The expandable frame 208 may include a system of one or more longitudinally extending ribbons 216A, 216B, 216C, 216D (collectively, ribbons 216), which may be arranged in a number of structural forms, such as an expandable basket. While the expandable frame 208 is illustrated as having four ribbons, it is contemplated that the frame 208 may include any number of ribbons desired, such as but not limited to one, two, three, five, or more. It is contemplated that while the term “ribbon” is used to describe the longitudinally extending portions of the flume 208, the ribbons 216 may be formed of any cross-sectional shape desired, such as, but not limited to circular, square, rectangular, oblong, polygonal, etc. For example, in some instances, the ribbons 216 may be formed of struts, wires, or filaments, or other suitable structures. The ribbons 216 may be attached together at their distal ends by a distal weld ball 218, further enclosed by distal hypotube 220, which collectively form a distal tip of the nerve modulation system 200. In some embodiments, the distal tip may additionally include spacers or other structure to maintain a desired radial spacing of the ribbons 216. The proximal ends of the ribbons 216 may be attached to the distal end 205 of the elongate shaft 211.

One skilled in the art will understand to make the distal tip atraumatic and flexible using a variety of techniques and materials known in the art for harmless navigation of the system 200 through the patient's vasculature. Moreover, expandable frame 208 may be configured fir expanding to a particular range of diameters based on the range of vessel sizes for standard and reliable system 200 positioning within various vessels.

Ribbons 216 may be arranged circumferentially around a central shaft 210 along the longitudinal axis of the expandable frame 208. In some instances, the distal ends of the ribbons 216 may be affixed to the distal end of the central shaft 210 and the distal. hypotube 220. The proximal end of the ribbons 216 may be attached to the distal end 205 of elongate shaft 211. To attach the ribbons 216, a variety of methods may be used, such as, but not limited to, stamping, welding, or reflow soldering. As will he discussed in more detail below, the central shaft 210 may assist the expansion of the expandable frame 208 through longitudinal movement of the central shaft 210. In some instances, the central shaft 210 may provide additional support to the expandable frame 208 during expansion.

Each ribbon 216 may include an intermediate region configured to contact the wall of the vessel. The intermediate region or wall-contact segments 222A, 222B, (collectively, wall-contact segments 222) may contact and align with walls 202 of the vessel upon expansion of the expandable frame 208. White not explicitly shown, it is contemplated that ribbons 216C and 216D may also include an intermediate region configured to contact the wall of the vessel. In some embodiments, the wall-contact segments 222 may be located generally at the center of ribbons 216, although this is not required. In the illustrated embodiment, the ribbons 216 may be shaped as generally flat strips, but a number of cross-sectional forms may be employed, such as circular, rectangular, square, etc., to provide variable stiffness to different portions of the ribbons. In some embodiments, the wall-contact segments 222 of the ribbons 216 may have higher stiffness relative to other portions of the ribbons 216 or other portions of the expandable is frame 208.

In some embodiments, the ribbons 216 may further include an electrode 224A, 224B, 224C, 224D (collectively, electrodes 224) positioned distal to the wall-contact segment 222 and an electrode 225A, 225B, 225C, 225D (collectively, electrodes 225), positioned proximal to the wall-contact segment 222 which may be used for radiofrequency (RF) ablation of the renal nerves. The illustrated embodiment includes two electrodes per ribbon (for example, electrodes 224A, 225A disposed on ribbon 216A), though it is contemplated that the modulation system 200 may include any number of electrodes 224, 225 per ribbon 216 as desired, such as, but not limited to, one, two, three, four, or more. It is contemplated that all the electrodes on a single ribbon may form a set of electrodes. For example, electrodes 224A and 224B may form a first set of electrodes. It is contemplated that the sets of electrodes may each include any desired number of electrodes, such as, but not limited to, one, two, three, four, or mote.

In some embodiments, the electrodes 224, 225 may be positioned adjacent to the ends of the ribbons 216. In one example, the electrodes 224 may be positioned at a location toward the distal end of a particular ribbon 216, while electrodes 225 may be positioned at a location toward its proximal end. In another example, the electrodes 224, 225 may be located radially inwards relative to the greatest radial extent of the expandable frame 208. Alternatively, the electrodes 224, 225 may be placed anywhere along the length of the ribbons 216 without departing from the scope and spirit of the present disclosure.

In some embodiments, each ribbon 216 may be configured to include pre-formed bend portions 226A, 226B, 226C, 226D (collectively bend portions 226) and 228A, 228B, 228C, 228D (collectively bend portions 228) positioned at various locations within. the ribbon. The location of the bend portions 226, 228 may depend upon the desired shape of the ribbons 216 after expansion of the expandable frame 208. It should be noted to that the position and preformed shape of bend portions 226, 228 largely determine the eventual shape of expandable frame 208. Employment of shape-memory materials, such as nitinol, may enhance the ability of the ribbons 216 to achieve exact configurations to fit various applications. One skilled in the art can contemplate that electrode segments 224, 225 may be positioned between bend portions 226, 228 and the distal and proximal ends of each ribbon 216.

It is further contemplated that the ribbons 216 may be formed such that the stiffness of each ribbon 216 varies over the length thereof. For example, the ribbons 216 may be formed such that the wall-contact segment 222 may be stiffer than the proximal or distal end regions of the ribbons 216. It is contemplated the size of the stiffer region may be selected to result in a desired outer diameter of the expandable frame 208.

In some instances, the expandable frame 208 may be made of an electrically conductive material, such as, but not limited to, nitinol. In some embodiments, the entire frame 208 may be coated with an insulating material, with discrete areas of insulation later removed to form electrically active regions. When so provided, these electrically active regions may define the electrodes. In other embodiments, the entire frame 208 may be formed of any material desired and may be coated with an insulating material. Discrete individual electrodes 224, 225 may be affixed to the insulating material of the frame 208 by any suitable means, such as welding, soldering, stamping, or use of adhesives. In some embodiments, the expandable frame 208 may include both electrically active regions formed by removing a portion of an insulating material as described above and discrete electrodes affixed to the insulating material. In some embodiments, the electrical current may be directly supplied to the expandable frame 208. In other instances, the modulation system 200 may include separate electrical. conductors for supplying energy to the electrodes 224, 225. As set out more completely below, spacing the electrode segments toward the ends of ribbons 216 allows the electrode segments to be spaced from the vessel wall 202 when the expandable frame 208 is deployed. The spacing from vessel wall 202 may be predetermined to provide optimal ablation effect.

Biocompatible materials such as suitable polymers or metals may be used to form the expandable frame 208 and its components such as, the ribbons 216, and the central to shaft 210. In general, suitable polymeric materials may include, but are not limited to, polyamide, polyether block amides, polyurethane, polyethylene, nylon, and polyethylene terephthalate. .Metallic materials, such as, but not limited to, stainless steel or nitinol may also be used. In addition, the expandable frame 208 may be insulated such that only the electrode segments 224 may not have insulation. This insulation may prevent unwanted current leakages from the frame 208. Methods that may be used to apply insulation include, but are not limited to, dip and spray coating, chemical vapor deposition, paryiene coating or by slipping tight fitting tubing over the ribbon such as using an electrically insulating shrink tubing.

The modulation system 200 may further include an actuation assembly 401 configured to shift the expandable frame 208 between an expanded configuration (FIGS. 2 and 5) and a collapsed configuration (FIG. 4). The actuation assembly 401 may include a central shaft 210 extending proximally from the distal end of expandable frame 208 and into the lumen 215 of the elongate shaft 211. The distal end of the central shaft 210 may be attached to the distal ends of the ribbons 216 by distal hypotube 220 or by any other suitable mechanism. The proximal end of the central shaft 210 may be attached to slidable piston 406. Proximal or distal actuation of the piston 406 may also actuate the distal end of the expandable frame 208 proximally or distally, In some instances, the actuation assembly 401 may include a biasing element 404, such as, but not limited to, a spring positioned between the distal end 205 of the elongate shaft 211 and the piston 406. In some instances, the distal end 205 of the elongate shaft 211 may include a flange or wall 207 extending generally orthogonal to the longitudinal axis of the elongate shaft 211. A distal end of the biasing element 404 may contact the wall 207 such that the biasing element 404 remains within the lumen 215 of the elongate shaft 211.

The biasing element 404 may have a first state in which no external forces are applied to the biasing element 404, as shown in FIG. 2. When the biasing element 404 is free from external forces, the biasing element 404 may urge the piston 406, and thus, also pulling the distal end of the expandable frame 208, proximally. Since the proximal ends of the ribbons 216 forming the frame are longitudinally fixed to the distal end 205 of the elongate shaft 211, the ribbons 216 may bow or flex outwards as the distal ends of the ribbons 216 are moved proximally to form an expanded frame 208. The expanded frame to 208 may have a greater outer diameter than the frame in the collapsed position (shown in FIG. 4). The biasing element 404 may have a second state in which an external force is applied to the biasing element 404 causing it to longitudinally compress. In some instances, a longitudinally extending control element 212 may be used to apply a distal force to the proximal side of the piston 406 causing the biasing element 404 to longitudinally compress, as shown in FIG. 4, biasing the piston 406 distally. While the biasing element 404 is referred to as having a first state and a second state, it should be understood that the biasing element 404 may be used in any number of lengths between the longest unstressed length and the shortest most stressed length. For example, in some instances, the biasing element 404 may not be fully compressed to maintain the expandable frame 208 in the collapsed configuration shown in FIG. 4. Further, while the control element 212 is described as applying a distal, pushing, force to the piston 406, it is contemplated that an opposite configuration may be used such that the a pulling force maintains the expandable frame 208 in a collapsed position. It is further contemplated that the modulation system 200 may be configured such that a pushing and/or pulling force may be applied to the piston 406 to the expand or contract the frame 208 beyond what the biasing element 404 provides.

It is contemplated that in order to maintain the ribbons 216 of the expandable frame in an elongated, relatively straight, collapsed position as shown in FIG. 4, a user may use the control element 212 to maintain pressure on the piston .406 and thus maintaining the expandable frame 208 in a collapsed state. In some embodiments, the control element 212 may be a control tube, formed of a hypotube. Other embodiments may include, but are not limited to, a control rod, or a control wire. The control element 212 may be adapted to be electrically conductive for providing electrical current to the electrodes 224, 225, For that task, the control element 212 may be connected to the power element 12 for providing electrical current to the central shaft 210. Exemplary methods of operating the renal nerve ablation system are discussed later with reference to FIGS. 4 and 5. In other embodiments, separate connections may be provided to conduct electrical power to electrodes 224, 225.

In some embodiments, the biasing element 404 may be formed from a shape memory material, such as, but not limited to nitinol, It is contemplated that the biasing element 404 may be heat set to elongate at a temperature above body temperature. As the modulation system 200 is advanced to the desired treatment region, the biasing element 404 may be in a generally compressed state, Once the expandable frame 208 is adjacent to a desired treatment region, the biasing element 404 may be heated, such as, but not limited to electrically heated, to cause the biasing element 404 to longitudinally expand. Longitudinal expansion of the biasing element 404 may cause the piston 406 to move proximally, thus causing the distal end of the expandable frame 208 to move proximally as well. Since the proximal ends of the ribbons 216 forming the frame are longitudinally fixed to the distal end 205 of the elongate shaft 211, the ribbons 216 may bow or flex outwards as the distal ends of the ribbons 216 are moved proximally to form an expanded frame 208. The expanded frame 208 may have a greater outer diameter than the frame in the collapsed position (shown in FIG. 4). In some instances, a control element 212 may not be necessary when the biasing element 404 is formed from a shape memory material. However, it is contemplated that the control element 212 may be provided to allow for additional force to be applied to the spring.

FIG. 3 illustrates the forces involved in expanding the expandable frame 208.

As noted above, in the compressed state, expandable frame 208 has a minimum diameter, and the actuation spring may be compressed. When restraint is removed, the spring begins acting on central shaft 210, pushing it proximally and in the process causing the ribbons to radially expand or bow out. Graph 300 shows exerted force on the frame 208 on the y-axis plotted against the resulting expandable frame diameter on the x-axis. Given a free-space environment, expansion of the frame would continue on curve A. At point P, however, expandable frame 208 makes contact with vessel wall 202, which resists further expansion of expandable frame 208. From that point onward, the force/diameter curve goes above curve A, moving toward point B.

At diameter D1, the expandable frame 208 has the same diameter as the inner diameter of the vessel wall 202, Further expansion of expandable frame 208 requires expansion of vessel wall 202, and it may be understood that expansion of tissue will at some point cause damage to that tissue. Here, diameter D2 represents the maximum expansion of vessel wall 202 that can be done without tissue damage while also placing the electrodes 224, 225 in the appropriate location with respect to the vessel wall 202 to provide an adequate treatment. Therefore, D1-D2 depicts an operating window, showing the maximum outer diameter of the expandable frame 208, within which the system 200 can operate safely and effectively. It is contemplated that the use of actuation assembly 401 may provide a consistent force to the expandable frame 208 regardless of the user. This may allow for the frame 208 to be consistently expanded to a desired outer diameter while minimizing risk of damage to the vessel wall.

FIGS. 4 and 5 illustrate aspects of an illustrative method for performing renal nerve ablation using the nerve modulation system 200 of FIG. 2 according to an embodiment of the present disclosure. In one embodiment, the nerve modulation system 200 includes an elongate shaft 211 having a distal opening 402, an expandable frame 208, a central shaft 210, and a control element 212 operating as described in connection with FIG. 2. In some embodiments, the elongate shaft 211 includes an actuation assembly 401 located proximal to the distal opening 402. However, the actuation assembly may be located at any suitable location proximal to the expandable frame 208, as may be contemplated by a person skilled in the art. The actuation assembly 401 may help to maintain the expandable frame 208 within desired operating window D1-D2, as previously discussed.

The actuation assembly includes a biasing element 404, which may be a coil spring, and a piston 406, which may be a flange element at the proximal end of central shaft 210. The biasing element 404 may be disposed between the distal end of the elongate shaft 211, which includes a wall 207 to hold the biasing element 404 within the shaft 211, and the piston 406. In the collapsed state of FIG. 4, the biasing element 404 may be maintained in a compressed position when a user pushes the control element 212 distally, as shown by arrow 230. When the user releases the control element 212, the biasing element 404 expands longitudinally due to stored energy of the compressed biasing element 404, thereby pushing the piston 406 central shaft 210 proximally and expanding the expandable frame 208, as shown by arrow 232 in FIG. 5. One skilled in the art will understand that the biasing element 404 may be configured such that a user is required to apply a pull force on the control element 212 to maintained the biasing element 404 in the collapsed state. Following this, the biasing element 404 may he configured to assume the expanded state when the user withdraws such pull force. Since, the actuation assembly 401 is located proximal to the distal tip of the system 200, friction along the elongate shaft 211 may be minimized, thereby allowing for direct force transmission between the biasing element 404 and the expandable frame 208 and therefore facilitating repeatable expansion results.

The user may either apply a mechanical or electrical push/pull force on the control element 212 depending on the type of control element 212 used to drive the actuation assembly 401 within the elongate shaft 211. In one embodiment, the control element 212 may be a control rod or plunger, which may be pushed mechanically by the user for driving the actuation assembly 401. In another embodiment, the control element 212 may be a control wire or any other conductive material, which is configured to electrically push the actuation assembly 401 within the elongate shaft 211 when provided with electrical current or voltage. Accordingly, the central shaft 210 may extend proximally/distally to shift the expandable frame 208 between the collapsed configuration and the expanded configuration.

The biasing element 404 may be made of a variety of biocompatible and shape-memory materials including, but are not limited to, nitinol. The biasing element 404 may be configured to any form such as helical, which can provide a control action for operating the expandable frame 208. The stiffness and length of the biasing element 404 may be chosen based on the operating window D1-D2 discussed in the description of FIG. 3 to allow a controlled longitudinal movement of the central shaft 210 for expansion of the expandable frame 208 where such expansion does not harm the vessel.

In the illustrated embodiment, the distal end of the biasing element 404 is maintained in position by the structure at the distal end of actuation assembly 401, which may have lip, flange, or crimped edge, or any similar structure as known in the art. Central shaft 210 extends into the lumen 215, terminating in a piston 406, with biasing element 404 acting on piston 406. It will be noted that when control element 212 is withdrawn, biasing element 404 only expands to its structural limit, and control element 212 may be out of contact with piston 406 at this point.

During operation, the nerve modulation system 200 may be introduced within the vessel while the system 200 is in a collapsed configuration. The nerve modulation system 200 may be configured to be introduced into the vessel through an incision or a suitable natural opening. In addition, the system 200 may be configured to be advanced to a desired location within the vessel with aid of a suitable introduction sheath, such as, the outer sheath 214, which may be part of an endoscope. The sheath 214 may include one or more working channels, which may be used to introduce a light source, a camera, an injector, or a morcellator in addition to the nerve modulation system 200.

The operator may maneuver the sheath 214 to a desired location within the vessel. While not explicitly shown, the modulation system 200 may further include temperature sensor/wire, an infusion lumen, radiopaque marker bands, fixed guidewire tip, a guidewire lumen, external sheath, and/or other components to facilitate the use and advancement of the sheath 214 within the vasculature.

During this process, the operator may use a visualization mechanism, such as fluoroscopy, to determine the location of the sheath 214 within the vessel. The expandable frame 208 may be configured to collapse for introduction into the vessel and to expand upon actuation. In order to keep the frame 208 in the collapsed configuration, a user either may mechanically or electrically, for example, push the control element 212 distally against the piston 406 to compress the biasing element 404 distally within the elongate shaft 211. After reaching the desired location, the frame 208 may be switched from a collapsed configuration to an expanded configuration. Accordingly, in one embodiment, the operator may withdraw the applied push force on the control element 212 to release the biasing element 404 such that the element 404 is allowed to expand proximally within the elongate shaft 211 via piston 406 along with the central shaft 210 extending proximally. Such proximal movement of the central shaft 210 may expand the expandable frame 208 due to operative connection between both ends of the ribbons 216 and the central shaft 210. In the expanded configuration, the expandable frame 208 expands to make contact with walls 202 of the vessel within allowable operating window D1-D2 discussed in the description of FIG. 3.

In some embodiments, once the expandable frame 208 is in contact with the vessel walls 202, the control element 212 can be used to provide the supply of electrical current to the central shaft 210, which in turn will convey the current to the electrodes 224, 225, In other embodiments, separate electrical conductors may supply the electrodes 224, 225 with the necessary electrical energy. The energized electrodes 224, 225 may ablate the nerves, veins, or other tissue variations, which are located. substantially proximate to the electrodes 224, 225, The number and size of the electrodes 224, 225 on the expandable frame 208 may determine the number of times the electrodes 224, 225 are required to be energized through the control element 212 for nerve ablation. Once a particular location has been ablated, it may be desirable to perform further ablation procedures at different locations. Once the expandable frame 208 has been repositioned within the vessel, energy may once again be delivered to the control element 212 and the electrodes 224, 225. In one example, if necessary, the electrodes 224, 225 may be rotated to perform ablation around the circumference of the expandable frame 208 at each electrode location. This process may be repeated at any number of longitudinal locations within the vessel as desired.

Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departure in form and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended. claims. 

What is claimed is:
 1. A system for nerve modulation, comprising: an elongate shaft having a proximal end, a distal end, and a lumen extending therebetween; an expandable frame positioned adjacent the distal end of the elongate shaft, the expandable frame configured to shift between an expanded configuration and a collapsed configuration, the expandable frame comprising: a proximal end and a distal end and a plurality of ribbons extending therebetween, at least one of the ribbons having an electrode positioned at a location radially inwards relative to the greatest radial extent of the expandable frame; and an expansion mechanism comprising: a biasing element positioned adjacent to the proximal end of the expandable frame; a piston movably disposed within the lumen of the elongate shaft, the piston positioned proximal to the distal end of the elongate shaft; a central shaft having a distal end attached to the distal end of the expandable frame and a proximal end attached to the piston; and a control element extending proximally from a proximal end of the piston.
 2. The system for nerve modulation of claim 1, wherein a central region of each ribbon is stiffer than a proximal end region and a distal end region of each ribbon.
 3. The system for nerve modulation of claim 1, wherein the biasing element is configured to move between a first compressed state and a second elongated state,
 4. The system for nerve modulation of claim 3, wherein movement of the biasing element between the first compressed state and the second elongated state shifts the expandable frame between the collapsed configuration and the expanded configuration.
 5. The system for nerve modulation of claim 1, wherein the biasing element is a spring.
 6. The system for nerve modulation of claim 1, wherein the control element includes a hypotube.
 7. The system for nerve modulation of claim 1, wherein the control element includes a pull wire.
 8. The system for nerve modulation of claim 1, wherein the biasing element includes a shape memory material.
 9. The system for nerve modulation of claim 1, wherein the control element is an electrical conductor.
 10. The system for nerve modulation of claim 1, wherein the biasing element is disposed between the distal end of the elongate shaft and the piston.
 11. A medical device assembly for nerve modulation, the assembly comprising: an elongate shaft having a proximal end, a distal end, and a lumen extending therebetween; an expandable frame configured to shift between an expanded configuration and a collapsed configuration, the expandable frame having a proximal end and a distal end and one or more ribbons attached therebetween; a biasing element disposed adjacent to the proximal end of the expandable frame; a piston movably disposed within the lumen of the elongate shall. and positioned adjacent to a proximal end of the biasing element; and a control element extending proximally from a proximal end of the piston.
 12. The medical device assembly of claim 11, wherein at least one of the one or ribbons includes an electrode.
 13. The medical device assembly of claim 11, wherein the biasing element is configured to move the expandable frame between the collapsed and the expanded configuration.
 14. The medical device assembly of claim 11, wherein the biasing element is disposed between the distal end of the elongate shaft and the piston.
 15. The medical device assembly of claim 11, wherein the control element is configured to exert a force on the piston that urges the piston distally.
 16. The medical device assembly of claim 11, wherein when the force on the piston is released, the biasing element urges the piston proximally.
 17. The medical device assembly of claim 11, wherein the biasing element des a spring.
 18. The medical device assembly of claim 11, wherein the control element includes a hypotube.
 19. The medical device assembly of claim 11, herein the control element includes a pull wire.
 20. A method for modulating renal nerves, the method comprising: advancing a system for nerve modulation within a renal blood vessel, the system for nerve modulation comprising: an elongate shaft having a proximal end, a distal end, and a lumen disposed therebetween; an expandable frame configured to shift between an expanded configuration and a collapsed configuration, the expandable frame having a proximal end and a distal end and a plurality of ribbons extending therebetween, at least one of the ribbons having an electrode positioned at a location radially inwards relative to the greatest radial extent of the expandable frame; and an expansion mechanism comprising: a biasing element positioned proximal to the proximal end of the expandable frame; a piston movably disposed adjacent to a proximal end of the biasing element, wherein movement of the piston controls a length of the biasing element; a central shaft having a distal end attached to the distal end of the expandable frame and a proximal end attached to the piston; and a control element extending proximally from a proximal end of the piston; wherein the expansion mechanism shifts the expandable frame between the expanded and the collapsed configuration; and maneuvering the elongate shaft to a desired location within the renal blood vessel; expanding the expandable frame; and ablating renal nerves perivascularly. 